Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide method and apparatus for video coding. In the method, prediction information of a current block in a current coding tree unit (CTU) from a coded video bitstream is decoded. The prediction information indicates an intra block copy (IBC) mode. Padded values of a reference block are determined based on a block vector that points to the reference block. The padded values of the reference block are copied from a reference sample line. At least a sample of the current block is reconstructed based on the padded values of the reference block.

INCORPORATION BY REFERENCE

This present application claims the benefit of priority to U.S.Provisional Application No. 62/788,935, “Intra picture blockcompensation with boundary padding” filed on Jan. 6, 2019, which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs of aneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding,” December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described herein is atechnique henceforth referred to as “spatial merge.”

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videocoding at a decoder. In an embodiment, a method of video coding at adecoder is provided. In the method, prediction information of a currentblock in a current coding tree unit (CTU) from a coded video bitstreamis decoded. The prediction information indicates an intra block copy(IBC) mode. Padded values of a reference block are determined based on ablock vector that points to the reference block. The padded values ofthe reference block are copied from a reference sample line. At least asample of the current block is reconstructed based on the padded valuesof the reference block.

In an embodiment, reconstructed samples of the reference block are notstored in a reference sample memory, and the padded values of thereference block are stored in a memory that is different from thereference sample memory.

In an embodiment, the current CTU is partitioned into a top-left codingregion, a top-right coding region, a bottom-left coding region, and abottom-right coding region, and the current block is in any one of thetop-left coding region, the top-right coding region, the bottom-leftcoding region, and the bottom-right coding region of the current CTU.

In an embodiment, the reference block is padded vertically by thereference sample line above the current CTU or horizontally by thereference sample line to the left of the current CTU.

In an embodiment, when a maximum size of the reference sample memory islimited to four sets of 64×64 luma samples and corresponding chromasamples, the reference sample memory stores reconstructed samples of acurrent 64×64 coding region and reconstructed samples of three 64×64reference coding regions, each of the three 64×64 reference codingregions being either in one of the current CTU and an adjacent left CTU,and the three 64×64 reference coding regions do not include all thereconstructed samples of the reference block.

In an embodiment, an adjacent left CTU is partitioned into a top-leftreference coding region, a top-right reference coding region, abottom-left reference coding region, and a bottom-right reference codingregion, and each of the reference coding regions in the left CTUincluding reconstructed samples that are not stored in the referencesample memory is padded by the reference sample line above the currentCTU or to the left of the current CTU.

In an embodiment, an adjacent left CTU is partitioned into a top-leftreference coding region, a top-right reference coding region, abottom-left reference coding region, and a bottom-right reference codingregion, and the reference block is included in the top-right referencecoding region or the bottom-right reference coding region of the leftCTU, or in the current CTU.

In an embodiment, when a maximum size of the reference sample memory islimited to three sets of 64×64 luma samples and corresponding chromasamples, the reference sample memory stores reconstructed samples of acurrent 64×64 coding region and reconstructed samples of two 64×64reference coding regions, each of the two 64×64 reference coding regionsbeing either in one of the current CTU and the left CTU, and the two64×64 reference coding regions do not include all the reconstructedsamples of the reference block.

In an embodiment, each of the top-right reference coding region of theleft CTU, the bottom-right reference coding region of the left CTU, andreference coding regions in the current CTU including reconstructedsamples that are not stored in the reference sample memory is padded bythe reference sample line above the current CTU or to the left of thecurrent CTU.

In an embodiment, when a maximum size of the reference sample memory islimited to two sets of 64×64 luma samples and corresponding chromasamples, the reference sample memory stores reconstructed samples of acurrent 64×64 coding region and reconstructed samples of one 64×64reference coding region in one of the current CTU or the left CTU, andthe 64×64 reference coding region includes all the reconstructed samplesof the reference block.

In an embodiment, each of the top-right reference coding region of theleft CTU, the bottom-right reference coding region of the left CTU, andreference coding regions in the current CTU including reconstructedsamples that are not stored in the reference sample memory is padded bythe reference sample line above the current CTU or to the left of thecurrent CTU.

In an embodiment, each of a plurality of reference coding regions of thecurrent CTU and an adjacent left CTU are padded horizontally by a firstreference sample line above the current CTU or vertically by a secondreference sample line to the left of the current CTU based on (i) afirst distance between each of the plurality of the reference codingregions and the first reference sample line above the current CTU and(ii) a second distance between each of the plurality of the referencecoding regions and the second reference sample line to the left of thecurrent CTU.

In an embodiment, the reference block is padded by boundary pixels of areconstructed reference block in one of the current CTU and an adjacentleft CTU, and reconstructed samples of the reconstructed reference blockare stored in the reference sample memory.

Aspects of the disclosure also provide an apparatus configured toperform any of the above methods. In an embodiment of the presentdisclosure, there is provided an apparatus. The apparatus includesprocessing circuitry. The processing circuitry is configured to decodeprediction information of a current block in a CTU from a coded videobitstream, the prediction information indicating an IBC mode. Theprocessing circuitry is configured to determine padded values of areference block based on a block vector that points to the referenceblock, the padded values of the reference block being copied from areference sample line. Further, the processing circuitry is configuredto reconstruct at least a sample of the current block based on thepadded values of the reference block.

Aspects of the disclosure also provide non-transitory computer-readablestorage mediums storing instructions which when executed by a computercause the computer to perform any of the above methods.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment of thepresent disclosure.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment of thepresent disclosure.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment of the present disclosure.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment of the present disclosure.

FIG. 6 shows a block diagram of an encoder in accordance with anembodiment of the present disclosure.

FIG. 7 shows a block diagram of a decoder in accordance with anembodiment of the present disclosure.

FIG. 8 is a schematic illustration of a current block in a currentpicture coded using intra block copy (IBC) in accordance with anembodiment of the present disclosure.

FIG. 9 shows an example of padding a nearest reference sample line abovea current coding tree unit (CTU) and padding another nearest referencesample line to the left of the current CTU in accordance with anembodiment of the present disclosure.

FIGS. 10A-10H show examples of boundary padding using IBC-basedcompensation with a memory storing four sets of reference samples inaccordance with some embodiments.

FIGS. 11A-11H show examples of boundary padding using IBC-basedcompensation with a memory storing three sets of reference samples inaccordance with some embodiments.

FIGS. 12A-12H show examples of boundary padding using IBC-basedcompensation with a memory storing two sets of reference samples inaccordance with some embodiments.

FIG. 13A shows an example of horizontal padding when decoding a currentcoding block in a top-left block of a current CTU in accordance with anembodiment.

FIG. 13B shows an example of hybrid padding when decoding a currentcoding block in a top-left block of a current CTU in accordance with anembodiment.

FIG. 13C shows an example of vertical padding when decoding a currentcoding block in a top-left block of a current CTU in accordance with anembodiment.

FIG. 14 shows an example of extending a reference area to a top CTU by Nrows in accordance with an embodiment.

FIG. 15 shows a flow chart outlining a decoding process (S1500)according to an embodiment of the disclosure.

FIG. 16 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

I. Video Coding Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers, and smartphones, but the principles of the present disclosure may be not solimited. Embodiments of the present disclosure find application withlaptop computers, tablet computers, media players, and/or dedicatedvideo conferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230), and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks, and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs), andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Intra Block Copy

A block can be coded using a reference block from a different or samepicture. Block based compensation using a reference block from adifferent picture can be referred to as motion compensation. Block basedcompensation using a reference block from a previously reconstructedarea within the same picture can be referred to as intra picture blockcompensation, current picture referencing (CPR), or intra block copy(IBC). A displacement vector that indicates the offset between thecurrent block and the reference block can be referred to as a blockvector (BV). Different from a motion vector in motion compensation,which can be any value (positive or negative, at either the x or ydirection), a BV is subject to constraints to ensure that the referenceblock has already been reconstructed and the reconstructed samplesthereof are available. In some embodiments, in view of parallelprocessing constraints, a reference area that is beyond certainboundaries (e.g., a tile boundary or wavefront ladder shape boundary) isexcluded.

The coding of a BV can be either explicit or implicit. In the explicitmode, the difference between a BV and its predictor can be signaled in amanner similar to an Advanced Motion Vector Prediction (AMVP) mode ininter coding. In the implicit mode, the BV can be recovered from only apredictor, for example in a similar way as a motion vector in mergemode. The resolution of a BV, in some implementations, is set to integerpositions or, in some examples, fractional positions.

The use of IBC at the block level can be signaled using a block levelflag (or IBC flag). In some examples, this flag can be signaled when thecurrent block is not coded in merge mode. In other examples, this flagcan be signaled by a reference index approach, for example, by treatingthe current decoded picture as a reference picture. Such a referencepicture can be placed in the last position of the list, such as in HEVCScreen Content Coding (HEVC SCC). This special reference picture canalso be managed together with other temporal reference pictures in theDecoded Picture Buffer (DPB).

While an embodiment of IBC is used as an example in the presentdisclosure, the embodiments of the present disclosure can be applied tovariations of IBC. The variations for IBC include, for example, flippedIBC where the reference block is flipped horizontally or verticallybefore being used to predict a current block, or line based IBC whereeach compensation unit inside an M×N coding block is an M×1 or 1×N line.

FIG. 8 is a schematic illustration of a current block (810) in a currentpicture (800) to be coded using IBC-based compensation in accordancewith an embodiment. In FIG. 8, an example of using IBC-basedcompensation is shown where the current picture (800) includes 15 blocksarranged into 3 rows and 5 columns. In some examples, each blockcorresponds to a coding tree unit (CTU). The current block (810)includes a sub-block (812) (e.g., a coding block in the CTU) that has ablock vector (822) pointing to a reference sub-block (832) in thecurrent picture (800).

The reconstructed samples of the current picture can be stored in amemory or memory block (e.g., a dedicated or designated memory orportion of memory). In consideration of implementation cost, thereference area where the reconstructed samples for reference blocksremain available may not be as large as an entire frame, depending on amemory size of the dedicated memory. Therefore, for a current sub-blockusing IBC-based compensation, in some examples, an IBC referencesub-block may be limited to only certain neighboring areas, but not theentire picture.

In one example, the memory size is limited to a size of one CTU, whichmeans the IBC mode can only be used when the reference block is withinthe same CTU as the current block. In another example, the memory sizeis limited to a size of two CTUs, which means the IBC mode can only beused when the reference block is either within the current CTU, or theCTU to the left of current CTU. When the reference block is outside theconstrained reference area (i.e., designated local area), even if it hasbeen reconstructed, the reference samples cannot be used for IBC-basedcompensation.

With the constrained reference area, the efficiency of IBC-basedcompensation is limited. There is a need to further improve theefficiency of IBC-based compensation with the constrained referencearea.

III. Block Partitioning in VVC

A picture may be divided into an array of non-overlapped CTUs, such asin VVC. The size of a CTU may be set to be 128×128 luma samples and thecorresponding chroma samples. The number of the corresponding chromasamples may depend on the color format. A CTU can be split into CUsusing one or a combination of tree splitting methods.

For example, a CTU can be split into CUs using a Quaternary-Tree (QT)split. This splitting method is the same as in HEVC for example. Eachparent block is split in half in both horizontal and verticaldirections. The resulting four smaller partitions are in the same aspectratio as its parent block. For example, in VVC, a CTU is first split byQT recursively. Each QT leaf node (in square shape) can be further splitrecursively using the multi-type (Binary-Tree and Ternary-Tree) tree asdescribed below. The Binary-Tree (BT) split refers to dividing theparent block in half in either a horizontal or vertical direction. Theresulting two smaller partitions are half in size as compared to theparent block. The Ternary-Tree (TT) split refers to dividing the parentblock in three parts in either a horizontal or vertical direction. Themiddle of the three parts is twice as large as the other two parts. Theresulting three smaller partitions are ¼, ½ and ¼ in size respectivelyas compared to the parent block.

The partition of a parent block may be constrained such that at a128×128 level, the following partitioning results for partitioning theparent block are allowed: 128×128, two 128×64, two 64×128, and four64×64. The partition of the parent block may be further constrained suchthat at a 128×64 or 64×128 level, the TT splits at either a horizontalor vertical direction are not allowed. In addition, if there is anyfurther split, the child blocks may be constrained to two 64×64 blocks.

The search range for IBC can be constrained within the current CTU wherea current coding block is located. A CTU size memory can be reused toeffectively extend the compensation range of IBC.

IV. Fixed Size Reference Search Range of Intra Block Copy with BoundaryPadding

Aspects of the present application provide methods to improve theIBC-based compensation performance under certain reference areaconstraints. Specifically, the size of a reference sample memory can beconstrained. For example, a maximum size of the reference sample memorycan be limited to N 64×64 luma samples and the corresponding chromasamples, where N may be 4, 3, or 2. The number of the correspondingchroma samples may depend on the color format. The methods describedherein can be extended to other values of N. Some methods have beenproposed regarding how to allocate the reference sample memory to storesome of previously decoded regions according to the location of acurrent coding block in a current CTU. In those methods, the searchrange for the IBC-based compensation depends on the location of thecurrent coding block in the current CTU. The previously decoded regionsthat are not stored in the reference sample memory cannot be used forreconstruction of a sample of current block.

FIG. 9 shows an example of padding a nearest reference sample line abovea current CTU to N rows above the current CTU and padding anothernearest reference sample line to the left of the current CTU to Mcolumns to the left of the current CTU according to an embodiment of thepresent disclosure. N and M may be positive integers. In FIG. 9, thenearest reference sample line (950) on top of the current CTU (910) andthe nearest reference sample line (970) to the left of the current CTU(910) may be stored in a memory for intra prediction of coding blocksnear the boundary of the current CTU (910). The memory may be differentfrom the reference sample memory described above.

An example of padding (e.g., extending or copying) the reference sampleline (950) on top of the current CTU to N rows and the reference sampleline (970) to the left CTU reference line to M columns is shown in FIG.9. Specifically, the current CTU (910) is partitioned into four 64×64blocks. The pixel values (i.e., reference sample values) of the nearestreference sample line (950) on top of the current CTU (910) are extendedto N rows above the current CTU (910). Similarly, the pixel values ofthe nearest reference sample line (970) to the left of the current CTU(910) are extended to M columns to the left of the current CTU (910).

Aspects of the present application provide methods that utilize boundarypadding in IBC-based compensation so that when block vectors point toreconstructed but unavailable reference areas, pixels values from anavailable reference area (e.g., the top reference sample line/leftreference sample line) may be extended vertically/horizontally to coverthose unavailable reference areas. Therefore, reconstructed samples inthe unavailable reference area can be represented by the padded valuesfor the IBC-based compensation. Accordingly, the search range of theIBC-based compensation can be increased as more BVs become valid.

A memory that stores reference samples of previously decoded CUs forfuture IBC-based compensation may be referred to as a reference samplememory. The reference sample memory can be a dedicated or designatedmemory, as described above.

According to some embodiments of the present disclosure, methods areproposed to improve IBC-based compensation performance under certainreference area constraints. More specifically, the size of a referencesample memory may be constrained. In the following discussion, the sizeof the reference sample memory may be fixed to be two set of (e.g.,64×64 sized) luma samples (together with corresponding chroma samples),three sets of (e.g., 64×64 sized) luma samples (together withcorresponding chroma samples), four sets of (e.g., 64×64 sized) lumasamples (together with corresponding chroma samples), or anothersuitable memory size. In one example, the size of the reference samplememory is a size of one CTU, such as one previously decoded CTU or oneleft CTU. In another example, the size of the reference sample memory isa size of two CTUs, such as two previously decoded CTUs or two leftCTUs, or one current CTU together with one left CTU. In someembodiments, each CTU requires a memory size for storing 128×128 lumasamples, together with corresponding chroma samples. When a referenceblock is outside the stored reconstructed areas, the reference blockcannot be used for the IBC-based compensation.

Embodiments of the present disclosure include methods for utilizing theone or more 64×64 sized reference sample memory blocks to optimize thesearch range of the IBC-based compensation.

The size of an IBC coded block can be as large as any regular intercoded block in general. In some embodiments of the present disclosure,in order to utilize the reference sample memory more efficiently, thesize of an IBC coded block can be limited to, for example, 64 lumasamples at either width or height edge and chroma samples withcorresponding size constraints, depending on the color format. The colorcan be, for example, in 4:2:0 format and the size of a chroma block inIBC mode may not be larger than 32 samples on each side. Lower limits,such as 32 luma samples on each side can be used as the size of the IBCcoded block. In the following discussion of the present disclosure, itis assumed that the maximum IBC coded block size is 64×64 luma samples.The block size of the corresponding chroma samples may depend on thecolor format, as described above. However, the methods described in thepresent disclosure can be performed in general without the limitsdescribed above.

Aspects of the present application include methods that utilize a fixedsize search range for IBC-based compensation. Specifically, boundarypadding in the IBC-based compensation may be used to extend pixel valuesfrom available reconstructed areas to the reconstructed but unavailablereference areas. In some embodiments of the present disclosure, pixelsvalues from a top reference sample line/left reference sample line maybe extended vertically/horizontally to cover those areas. Therefore, thereconstructed samples in an unavailable reference area can berepresented by the padded values for the IBC-based compensation.Accordingly, the search range of the IBC mode can be increased as moreBVs become valid.

In an embodiment of the present disclosure, all reconstructed referencesamples in a current CTU and an entire left CTU of the current CTU canbe used as the search range. For example, the current and left CTUs canbe used as the search range for a current coding block in the currentCTU for the IBC-based compensation, regardless of the location of thecurrent coding block in the current CTU. The left CTU may be adjacent tothe current CTU. For example, in FIGS. 10A-10H, the areas that have beenreconstructed but not available for reference due to the limited localreference sample memory size are padded by one or more reference samplelines from a top CTU above the left CTU. The padding can be performedwith one or more reference sample lines from other CTUs (e.g., a CTU tothe left of the left CTU) in other embodiments.

FIGS. 10A-10D illustrate examples of reference sample memory usage forthe IBC-based compensation and boundary padding for unavailablereference areas when four sets of (e.g., 64×64 sized) sized referencesample memory blocks are used and when a quadtree or horizontal binarytree split (e.g., at a 128×128 level) is used. FIGS. 10E-10H illustrateexamples of reference sample memory usage for the IBC-based compensationand boundary padding for unavailable reference areas when four sets of(e.g., 64×64 sized) reference sample memory blocks are used and when avertical binary tree split (e.g., at a 128×128 level) is used.

In FIGS. 10A-10H, one of the four sets of (e.g., 64×64 sized) referencesample memory blocks may be used to store reconstructed samples of thecurrent 64×64 coding region, and the other three sets of (e.g., 64×64sized) reference sample memory blocks may be used to store reconstructedsamples of previously decoded 64×64 coding regions. Each of the areaswith vertical stripes is a 64×64 region where the current coding blockis located, which is marked with 0, 1, 2, or 3 respectively depending onthe location of the current coding block. Each of the shaded areas is apreviously decoded and reconstructed area. Each of the reconstructed butunavailable reference areas is a shaded area with an X mark. Padding ofthe CTU boundary reference samples are applied to the reconstructed butunavailable reference areas (areas with dotted arrows).

The search range may not always be the same for the current coding blocklocated in each of the four 64×64 coding regions in the current CTU ascertain reference areas may be unavailable. Specifically, the searchrange for the current coding block in the current CTU may depend on thelocation of the current coding block in the current CTU. However, afterperforming vertical padding on the unavailable reference areas, thesearch range for the current coding block in the current CTU can beextended to the entire left CTU and the reconstructed areas of thecurrent CTU regardless of the location of the current coding block inthe current CTU.

For example, as shown in FIG. 10A and FIG. 10E, when the current codingblock is at a top-left block of the current CTU (1001, 1013), the searchrange may include a top-right block, a bottom-left block, and abottom-right block of the left CTU (1002, 1014). The search range mayfurther include reconstructed areas in the current CTU (1001, 1013) insome embodiments. The search range may not include a top-left block ofthe left CTU (1002, 1014) due to the size of the reference samplememory. In some examples, vertical padding may be used to copy thepixels values of a reference sample line (1003, 1015) from a top CTU tothe top-left block of the left CTU (1002, 1014). The padded pixel valuesmay be stored in a memory different from the reference sample memory.The memory may be used for intra prediction of the coding blocks nearthe boundary of the current CTU. Therefore, after the padding, thesearch range for the current coding block in the current CTU (1001,1013) may be the entire left CTU (1002, 1014) and the reconstructedareas of the current CTU (1001, 1013).

In FIG. 10B, when a quadtree or horizontal binary tree split at (e.g., a128×128 level) is used and when the current coding block is at atop-right block of the current CTU (1004), the search range may includea top-left block of the current CTU (1004), and a bottom-left block anda bottom-right block of the left CTU (1005). The search range mayfurther include reconstructed areas in the current CTU (1004) in someembodiments. A top-left block and a top-right block of the left CTU(1005) may not be available due to the size of the reference samplememory. In some examples, vertical padding may be used to copy thepixels values of a reference sample line (1006) from a top CTU to thetop-left block and the top-right block of the left CTU (1005). Thepadded pixel values may be stored in a memory different from thereference sample memory. The memory may be used for intra prediction ofthe coding blocks near the boundary of the current CTU. Therefore, afterthe padding, the search range for the current coding block in thecurrent CTU (1004) may include the entire left CTU (1005) and thereconstructed areas of the current CTU (1004).

In FIG. 10C, when a quadtree or horizontal binary tree split (e.g., at a128×128 level) is used and when the current coding block is at abottom-left block of the current CTU (1007), the search range mayinclude a top-left block and a top-right block of the current CTU(1007), and a bottom-right block of the left CTU (1008). The searchrange may further include reconstructed areas in the current CTU (1007)in some embodiments. A top-left block, a top-right block, and abottom-left block of the left CTU (1008) may not be available due to thesize of the reference sample memory. In some examples, vertical paddingmay be used to copy the pixels values of a reference sample line (1009)from a top CTU to the top-left block, the top-right block, and thebottom-left block of the left CTU (1008). The padded pixel values may bestored in a memory different from the reference sample memory. Thememory may be used for intra prediction of the coding blocks near theboundary of the current CTU (1007). Therefore, after the padding, thesearch range for the current coding block in the current CTU (1007) mayinclude the entire left CTU (1008) and the reconstructed areas of thecurrent CTU (1007).

In FIG. 10F, when a vertical binary tree split (e.g. at a 128×128 level)is used and when the current coding block is at a bottom-left block ofthe current CTU (1016), the search range may include a top-left block ofthe current CTU (1016), and a top-right block, and a bottom-right blockof the left CTU (1017). The search range may further includereconstructed areas in the current CTU (1016) in some embodiments. Atop-left block and a bottom-left block of the left CTU (1017) may not beavailable due to the size of the reference sample memory. In someexamples, vertical padding may be used to copy the pixels values of areference sample line (1018) from a top CTU to the top-left block andthe bottom-left block of the left CTU (1017). The padded pixel valuesmay be stored in a memory different from the reference sample memory.The memory may be used for intra prediction of the coding blocks nearthe boundary of the current CTU (1016). Therefore, after the padding,the search range for the current coding block in the current CTU (1016)may include the entire left CTU (1017) and the reconstructed areas ofthe current CTU (1016).

In FIG. 10G, when a vertical binary tree split (e.g., at a 128×128level) is used and when the current coding block is at a top-right blockof the current CTU (1019), the search range may include a top-leftblock, a bottom-left block of the current CTU (1019), and a bottom-rightblock of the left CTU (1020). The search range may further includereconstructed areas in the current CTU (1019) in some embodiments. Atop-left block, a top-right block, and a bottom-left block of the leftCTU (1020) may not be available due to the size of the reference samplememory. In some examples, vertical padding may be used to copy thepixels values of a reference sample line (1021) from a top CTU to thetop-left block, the top-right block, and the bottom-left block of theleft CTU (1020). The padded pixel values may be stored in a memorydifferent from the reference sample memory. The memory may be used forintra prediction of the coding blocks near the boundary of the currentCTU (1019). Therefore, after the padding, the search range for thecurrent coding block in the current CTU (1019) may include the entireleft CTU (1020) and the reconstructed areas of the current CTU (1019).

In FIGS. 10D and 10H, when the current coding block is at a bottom-rightblock of the current CTU (1010, 1022), the search range may include atop-left block, a bottom-left block, and a top-right block of thecurrent CTU (1010, 1022). The search range may further includereconstructed areas in the current CTU (1010, 1022) in some embodiments.The entire left CTU (1011 and 1023) may not be available due to the sizeof the reference sample memory. In some examples, vertical padding maybe used to copy the pixels values of a reference sample line (1012,1024) from a top CTU to the entire left CTU (1011, 1023). The paddedpixel values may be stored in a memory different from the referencesample memory. The memory may be used for intra prediction of the codingblocks near the boundary of the current CTU (1010, 1022). Therefore,after the padding, the search range for the current coding block in thecurrent CTU (1010, 1022) may include the entire left CTU (1011, 1023)and the reconstructed areas of the current CTU (1010, 1022).

In an embodiment of the present disclosure, all reconstructed referencesamples in a current CTU and a right half (e.g., 64×128 area) part of aleft CTU of the current CTU can be used as the search range, regardlessof the location of a current coding block in the current CTU. The leftCTU may be adjacent to the current CTU. Areas that have beenreconstructed but not available for reference due to a limited localreference sample memory size may be padded by a reference sample linefrom a neighboring CTU, such as a top CTU of the current CTU or the leftCTU, or a reference sample line from the left CTU.

FIGS. 11A-11D illustrate examples of reference sample memory usage forthe IBC-based compensation and boundary padding for an unavailablereference area when three sets of (e.g., 64×64 sized) reference samplememory blocks are used and when a quadtree or horizontal binary treesplit at a 128×128 level is used. FIGS. 11E-11H illustrate examples ofreference sample memory usage for the IBC-based compensation andboundary padding for the unavailable reference area when three sets of(e.g., 64×64 sized) reference sample memory blocks are used and when avertical binary tree split at a 128×128 level is used. One of the threesets of (e.g., 64×64 sized) reference sample memory blocks may be usedto store reconstructed samples of the current (e.g., 64×64 sized) codingregion, and the other two sets of (e.g., 64×64 sized) reference samplememory blocks may be used to store reconstructed samples of previouslydecoded 64×64 coding regions.

In FIGS. 11A-11H, each of the areas with vertical strips is a 64×64region where the current coding block is located. Each of the shadedareas is a previously decoded and reconstructed area. The areassurrounded by a dotted rectangle include the reconstructed areas and the64×64 current coding regions. The references samples in the areassurrounded by a dotted rectangle are stored in a reference samplememory. Padding of CTU boundary reference samples may be applied to thereconstructed but unavailable reference areas (areas with dotted arrows)so that the search range can always include at least the right half ofthe left CTU and the reconstructed areas in the current CTU.

For example, as shown in FIGS. 11A and 11E, when the current codingblock is at a top-left block of the current CTU (1101, 1112), the searchrange may include a top-right block and a bottom-right block of theright half of the left CTU (1102, 1113). The search range may furtherinclude reconstructed areas in the current CTU (1102, 1113) in someembodiments. Padding may not need to be performed in this examplebecause the reconstructed reference samples in the right half of theleft CTU (1102, 1113) are still stored in the reference sample memoryand block vectors that point to the right half of the left CTU (1102 and1113) are valid.

In FIG. 11B, when a quadtree or horizontal binary tree split (e.g., at a128×128 level) is used and when the current coding block is at atop-right block of the current CTU, the search range may include atop-left block of the current CTU (1103) and a top-right block of theright half of the left CTU (1104). The search range may further includereconstructed areas in the current CTU (1103) in some embodiments. Abottom-right block of the right half of the left CTU (1104) may not beavailable due to the size of the reference sample memory. In someexamples, horizontal padding may be used to copy the pixels values of areference sample line (1105) from the right half of the left CTU (1104)that is nearest to the current CTU (1103) to the bottom-right block ofthe right half of the left CTU (1104). The padded pixel values may bestored in a memory different from the reference sample memory. Thememory may be used for intra prediction of the coding blocks near theboundary of the current CTU (1103). Therefore, after the padding, thesearch range for the current coding block in the current CTU (1103) mayinclude the right half of the left CTU (1104) and the reconstructedareas of the current CTU (1103).

In FIG. 11C, when a quadtree or horizontal binary tree split (e.g., at a128×128 level) is used and when the current coding block is at abottom-left block of the current CTU (1106), the search range mayinclude a top-left block and a top-right block of the current CTU(1106). The search range may further include reconstructed areas in thecurrent CTU (1106) in some embodiments. A top-right block and abottom-right block of the right half of the left CTU (1107) may not beavailable due to the size of the reference sample memory. In someexamples, horizontal padding may be used to copy the pixels values of areference sample line (1108) from the right half of the left CTU (1107)that is nearest to the current CTU (1106) to the top-right block and thebottom-right block of the right half of the left CTU (1107). The paddedpixel values may be stored in a memory different from the referencesample memory. The memory may be used for intra prediction of the codingblocks near the boundary of the current CTU (1107). Therefore, after thepadding, the search range for the current coding block in current CTU(1107) may include the right half of the left CTU (1107) and thereconstructed areas of the current CTU (1107).

In FIG. 11F, when a vertical binary tree split (e.g., at a 128×128level) is used and when the current coding block is at a bottom-leftblock of the current CTU (1114), the search range may include a top-leftblock of the current CTU (1114) and a top-right block of the right halfof the left CTU (1115). The search range may further includereconstructed areas in the current CTU (1114) in some embodiments. Abottom-right block of the right half of the left CTU (1115) may not beavailable due to the size of the reference sample memory. In someexamples, horizontal padding may be used to copy the pixels values of areference sample line (1116) from the right half of the left CTU (1115)that is nearest to the current CTU (1114) to the bottom-right block ofthe left CTU (1115). The padded pixel values may be stored in a memorydifferent from the reference sample memory. The memory may be used forintra prediction of the coding blocks near the boundary of the currentCTU (1114). Therefore, after the padding, the search range for thecurrent coding block in the current CTU (1114) may be the right half ofthe left CTU (1115) and the reconstructed areas of current CTU (1114).

In FIG. 11G, when a vertical binary tree split (e.g., at a 128×128level) is used and when the current coding block is at a top-right blockof the current CTU (1117), the search range may include a top-left blockand a bottom-left block of the current CTU (1117). The search range mayfurther include reconstructed areas in the current CTU (1117) in someembodiments. A top-right block and a bottom-right block of the righthalf of the left CTU (1118) may not be available due to the size of thereference sample memory. In some examples, horizontal padding may beused to copy the pixels values of a reference sample line (1119) fromthe right half of the left CTU (1118) that is nearest to the current CTU(1117) to the top-left block and the bottom-right block of the righthalf of the left CTU (1118). The padded pixel values may be stored in amemory different from the reference sample memory. The memory may beused for intra prediction of the coding blocks near the boundary of thecurrent CTU (1117). Therefore, after the padding, the search range forthe current coding block in the current CTU (1117) may include the righthalf of the left CTU (1118) and the reconstructed areas of the currentCTU (1117).

In FIGS. 11D and 11H, when the current coding block is at a bottom-rightblock of the current CTU (1109, 1120), the search range may include atop-right block and a bottom-left block of the current CTU (1109, 1120).The search range may further include reconstructed areas in the currentCTU (1109, 1120) in some embodiments. A top-left block of the currentCTU (1109, 1120), and a top-right block and a bottom-right block of theright half of the left CTU (1110, 1121) due to the size of the referencesample memory. In some examples, horizontal padding may be used to copythe pixels values of a reference sample line (1111, 1122) from the righthalf of the left CTU (1110, 1121) that is nearest to the current CTU(1109,1120) to the top-left block of the current CTU (1109, 1120), andthe top-right block and the bottom-right block of the right half of theleft CTU (1110,1121). The padded pixel values may be stored in a memorydifferent from the reference sample memory. The memory may be used forintra prediction of the coding blocks near the boundary of the currentCTU (1109, 1120). Therefore, after the padding, the search range for thecurrent coding block in the current CTU (1109, 1120) may include theright half of the left CTU (1110, 1121) and the reconstructed areas ofcurrent CTU (1109, 1120).

According to an embodiment of the present disclosure, FIGS. 12A-12Ddescribe an example of reference sample memory usage for the IBC-basedcompensation and boundary padding for the unavailable reference areawhen two sets of (e.g., 64×64 sized) reference sample memory blocks areused and when a quadtree or horizontal binary tree split (e.g., at a128×128 level) is used. FIGS. 12E-12H describe an example of referencesample memory usage for the IBC-based compensation and boundary paddingfor the unavailable reference area when two sets of (e.g., 64×64 sized)reference sample memory blocks are used and when vertical binary treesplit (e.g., at a 128×128 level) is used. One of the two sets ofreference sample memory blocks may be used to store reconstructedsamples of the current coding region, and the other set of referencesample memory block may be used to store reconstructed samples of apreviously decoded coding region.

In FIGS. 12A-12H, each of the areas with vertical stripes is a region(e.g., 64×64 region) where the current coding block is located. Each ofthe shaded areas is a previously decoded and reconstructed area. Theareas surrounded by a dotted rectangle include the reconstructed areasand the current coding region (e.g., 64×64 current coding region). Thereferences samples in the areas surrounded by the dotted rectangle arestored in the reference sample memory. Padding of CTU boundary referencesamples may be applied to the reconstructed but unavailable areas (areaswith dotted arrows) so that the search range can always include theright half of a left CTU of the current CTU and the reconstructed areasin the current CTU. The left CTU may be adjacent to the current CTU.

For example, as shown in FIGS. 12A and 12E, when the current codingblock is at a top-left block of the current CTU (1201, 1213), the searchrange may include a top-right block of the right half of the left CTU(1202, 1214). The search range may further include reconstructed areasin the current CTU (1201, 1213) in some embodiments. A bottom-rightblock of the right half of the left CTU (1202, 1214) may not beavailable due to the size of the reference sample memory. In someexamples, horizontal padding may be used to copy the pixels values of areference sample line (1203, 1215) from the right half of the left CTU(1202, 1214) that is nearest to the current CTU (1201, 1213) to thebottom-right block of the right half of the left CTU (1202, 1214). Thepadded pixel values may be stored in a memory different from thereference sample memory. The memory may be used for intra prediction ofthe coding blocks near the boundary of the current CTU (1201, 1213).Therefore, after the padding, the search range for the current codingblock in the current CTU (1201, 1213) may include the right half of theleft CTU (1202, 1214) and the reconstructed areas of the current CTU(1201, 1213).

In FIG. 12B, when a quadtree or horizontal binary tree split (e.g., at a128×128 level) is used and when the current coding block is at atop-right block of the current CTU (1204), the search range may includea top-left block of the current CTU (1204). The search range may furtherinclude reconstructed areas in the current CTU (1204) in someembodiments. A top-right block and a bottom-right block of the righthalf of the left CTU (1205) may not be available due to the size of thereference sample memory. In some examples, horizontal padding may beused to copy the pixels values of a reference sample line (1206) fromthe right half of the left CTU (1205) that is nearest to the current CTU(1204) to the top-right block and the bottom-right block of the righthalf of the left CTU (1205). The padded pixel values may be stored in amemory different from the reference sample memory. The memory may beused for intra prediction of the coding blocks near the boundary of thecurrent CTU (1204). Therefore, after the padding, the search range forthe current coding block in the current CTU (1204) may include the righthalf of the left CTU (1205) and the reconstructed areas of the currentCTU (1204).

In FIG. 12C, when a quadtree or horizontal binary tree split (e.g., at a128×128 level) is used and when the current coding block is at abottom-left block of the current CTU (1207), the search range mayinclude a top-right block of the current CTU (1207). The search rangemay further include reconstructed areas in the current CTU (1207) insome embodiments. A top-left block of the current CTU (1207), and atop-right block and the bottom-right block of the right half of the leftCTU (1208) may not be available due to the size of the reference samplememory. In some examples, horizontal padding may be used to copy thepixels values of a reference sample line (1209) from the right half ofthe left CTU (1208) that is nearest to the current CTU (1207) to thetop-left block of the current CTU (1207), and the top-right block andthe bottom-right block of the right half of the left CTU (1208). Thepadded pixel values may be stored in a memory different from thereference sample memory. The memory may be used for intra prediction ofthe coding blocks near the boundary of the current CTU (1207).Therefore, after the padding, the search range for the current codingblock in current CTU (1207) may include the right half of the left CTU(1208) and the reconstructed areas of the current CTU (1207).

In FIG. 12F, when a vertical binary tree split (e.g., at a 128×128level) is used and when the current coding block is at a bottom-leftblock of the current CTU (1219), the search range may include a top-leftblock of the current CTU (1219). The search range may further includereconstructed areas in the current CTU (1219) in some embodiments. Atop-right block and a bottom-right block of the right half of the leftCTU (1220) may not be available due to the size of the reference samplememory. In some examples, horizontal padding may be used to copy thepixels values of a reference sample line (1221) from the right half ofthe left CTU (1220) that is nearest to the current CTU (1219) to thetop-right block and the bottom-right block of the right half of the leftCTU (1220). The padded pixel values may be stored in a memory differentfrom the reference sample memory. The memory may be used for intraprediction of the coding blocks near the boundary of the current CTU(1219). Therefore, after the padding, the search range for the currentcoding block in the current CTU (1219) may include the right half of theleft CTU (1220) and the reconstructed areas of current CTU (1219).

In FIG. 12G, when a vertical binary tree split (e.g., at a 128×128level) is used and when the current coding block is at a top-right blockof the current CTU (1219), the search range may include a top-left blockof the current CTU (1219). The search range may further includereconstructed areas in the current CTU (1219) in some embodiments. Abottom-left block of the current CTU (1219), and a top-right block and abottom-right block of the right half of the left CTU (1220) may not beavailable due to the size of the reference sample memory. In someexamples, horizontal padding may be used to copy the pixels values of areference sample line (1221) from the right half of the left CTU (1220)that is nearest to the current CTU (1219) to the bottom-left block ofthe current CTU (1219), and the top-right block and the bottom-rightblock of the left CTU (1220). The padded pixel values may be stored in amemory different from the reference sample memory. The memory may beused for intra prediction of the coding blocks near the boundary of thecurrent CTU (1219). Therefore, after the padding, the search range forthe current coding block in the current CTU (1219) may include the righthalf of the left CTU (1220) and the reconstructed areas of the currentCTU (1219).

In FIGS. 12D and 12H, when the current coding block is at thebottom-right block of the current CTU (1210, 1222), the search range mayinclude a top-right block of the current CTU (1210, 1222). The searchrange may further include reconstructed areas in the current CTU (1210,1222) in some embodiments. A top-left block and a bottom-left of thecurrent CTU (1210, 1222), and a top-right block and a bottom-right blockof the right half of the left CTU (1211, 1223) may not be available dueto the size of the reference sample memory. In some examples, horizontalpadding may be used to copy the pixels values of a reference sample line(1212, 1224) from the right half of the left CTU (1211, 1223) that isnearest to the current CTU (1210, 1222) to the top-left block and thebottom-left of the current CTU (1210, 1222), and the top-right block andthe bottom-right block of the right half of the left CTU (1211, 1223).The padded pixel values may be stored in a memory different from thereference sample memory. The memory may be used for intra prediction ofthe coding blocks near the boundary of the current CTU (1210, 1222).Therefore, after the padding, the search range for the current codingblock in the current CTU (1210, 1222) may include the right half of theleft CTU (1211, 1223) and the reconstructed areas of current CTU (1210,1222).

One or a combination of horizontal padding from reconstructed samples ata rightmost column of a left CTU, or vertical padding from reconstructedsamples at a bottommost row of a top CTU may be used to fill theunavailable reference area for the IBC-based compensation. In someexamples, vertical padding is always used, as shown in FIGS. 10A-10H. Inother examples, horizontal padding is always used, as shown in FIGS.11B-11D, FIGS. 11F-11H, and FIGS. 12A-12H.

In an embodiment of the present disclosure, both vertical and horizontalpadding may be used in decoding a current block in a current CTU usingthe IBC-based compensation. For example, in FIGS. 10C and 10D, when aquadtree or horizontal split (e.g., at a 128×128 level) is used,reconstructed samples in the top-right 64×64 block of the left CTU maynot be available for reference. The top-right 64×64 block of the leftCTU may be padded from a reference sample line in a top CTU.Alternatively, the top-right 64×64 block of the left CTU may be paddedfrom a reference sample line at the rightmost column of left CTU. Anaverage or weighted average of the reference sample lines of differentCTUs can be used for padding in other embodiments. Similar examples mayapply to other reconstructed but unavailable areas.

In an embodiment of the present disclosure, aspects of the presentdisclosure provide that the reference blocks of a current CTU may comefrom the same region (e.g., 64×64 region) in the picture.

In an embodiment, all the block vectors in a current CTU may point toonly reference blocks that are available without padding. In otherwords, all of the reference samples of the reference blocks that arepointed to by block vectors are stored in a reference sample memory.Alternatively, all the block vectors in the current CTU may point toonly reference blocks that are padded. In other words, all of thereference samples of the reference blocks that are pointed to by blockvectors are stored in a memory (e.g., a temporary memory) different fromthe reference sample memory. In an embodiment, the encoder may berequired to generate a bitstream with BV values such that a referenceblock is either reconstructed entirely from the reference sample memory(e.g., the reference block is fully available without any padding) orfully from padded samples. If the BV values are not valid (e.g., notwithin a certain range), then the encoder fails to conform to thisrequirement. By applying this constraint/requirement, at the decoderside, the reconstruction of a prediction block can be easier byaccessing only the reference sample memory or only the temporary memoryinstead of accessing both the reference sample memory and the temporarymemory.

According to aspects of the present disclosure, vertical and horizontalpadding may be used together to decode a current block in a current CTUusing the IBC-based compensation. Vertical and horizontal padding for areference coding region may be used based on distance to a CTU boundary,such as (i) a first distance between the reference coding region and areference sample line above the current CTU and (ii) a second distancebetween the reference coding region and another reference sample line tothe left of the current CTU. In one embodiment, a padding method whichuses spatially closer pixel values for the pixels to be padded is used.For example, if the first distance is shorter than the second distance,then vertical padding using the reference sample line above the currentCTU may be used for the reference coding region. If the first distanceis longer than the second distance, then horizontal padding using theother reference sample line to the left of the current CTU may be usedfor the reference coding region. One of the horizontal padding andvertical padding can be selected by default when the first and seconddistances are equal to each other.

In one embodiment, when the first distance is the same as the seconddistance, vertical padding may be always used. In another embodiment,horizontal padding may be always used when the first distance is thesame as the second distance.

In one embodiment of the present disclosure, padding can be implementedby using the boundary pixels of an edge of the available referencerange, instead of using the reference sample line at the rightmostcolumn in a left CTU or another reference sample line at the bottommostrow in a top CTU. For example, FIG. 13A shows padding the top leftregion (e.g., a 64×64 region) of the left CTU (1320) using the rightmostcolumn line of the left CTU (1320). However, a reference sample line inthe reconstructed and available area (e.g., the leftmost referencesample line (1330) of the top-right 64×64 block of the left CTU (1320))may be used to extend vertically to pad the top-left 64×64 block of theleft CTU (1320).

In one embodiment of the present disclosure, the padding range can beextended to the entire left CTU, or other different sizes when theavailable reference range includes only a portion of the left CTU. Forexample, the left half (left 64×128) part of the left CTU can be paddedby horizontal padding, vertical padding, or a combination of horizontalpadding and vertical padding for examples described in FIGS. 12A-12H.Specifically, as shown in FIG. 13A, when the current coding block islocated in the top-left block of the current CTU (1310) and the searchrange only includes the top-right block of the left CTU (1320) and, insome embodiments, the current coding block of the current CTU (1310),the top-left block, the bottom-left block, and the bottom-right block ofthe left CTU (1320) can be padded horizontally using a reference sampleline at the rightmost column of the left CTU (1320).

FIG. 13B shows padding the top-left block, the bottom-left block, andthe bottom-right block of the left CTU (1350) by a hybrid padding (i.e.,a combination of horizontal and vertical padding) when decoding acurrent coding block in a top-left block of the current CTU (1340) andwhen the search range only includes the top-right block of the left CTU(1350) and, in some embodiments, the current coding block of the currentCTU (1340). In FIG. 13B, the top-left block and the bottom-left block ofthe left CTU (1350) may be padded vertically using a reference sampleline on top of the left CTU (1350) and the bottom-right block of theleft CTU (1350) may be padded horizontally using another referencesample line (e.g., a reference sample line at the rightmost column ofthe left CTU (1350)).

FIG. 13C shows padding the top-left block, the bottom-left block, andthe bottom-right block of the left CTU (1370) by vertical padding usinga reference sample line on top of the left CTU (1370) when decoding acurrent coding block in a top-left block of the current CTU (1360) andwhen the search range only includes the top-right block of the left CTU(1370) and, in some embodiments, the current coding block of the currentCTU (1360).

The padding range can be extended to regions of another CTU (e.g., in atop CTU (1430)), as shown in FIG. 14. The top CTU may be above a currentCTU (1410) and a left CTU (1420). In FIG. 14, when decoding a currentcoding block in a top-left block of the current CTU (1410), pixel valuesof the reference sample line (1440) in the top CTU (1430) can beextended to the left half region of the left CTU (1420). Further, pixelvalues of the reference sample line (1440) in the top CTU (1430) can beextended to N rows in the top CTU (1430). N may be a positive integer.

FIG. 15 shows a flow chart outlining a decoding process (1500) accordingto an embodiment of the disclosure. The process (1500) can be used todecode a block (i.e., a current coding block) in a current CTU of apicture using the IBC-based compensation. In some embodiments, one ormore operations are performed before or after process (1500), and someof the operations illustrated in FIG. 15 may be reordered or omitted. Invarious embodiments, the process (1500) is executed by processingcircuitry, such as the processing circuitry in the terminal devices(210), (220), (230), and (240), the processing circuitry that performsfunctions of the video decoder (310), (410), or (710), and the like. Insome embodiments, the process (1500) is implemented by softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1500). Theprocess starts at (S1501) and proceeds to (S1510).

At (S1510), prediction information of a current block in a currentcoding tree unit (CTU) from a coded video bitstream is decoded. Theprediction information indicates an intra block copy (IBC) mode.

At (S1520), padded values of a reference block are determined based on ablock vector that points to the reference block. The padded values ofthe reference block are copied from a reference sample line. In someexamples, the reference samples of the reference block may not be storedin a reference sample memory. The reference sample memory may only storetwo sets, three sets, or four sets of 64×64 luma samples andcorresponding chroma samples. When the reference samples of referenceblock is not stored in the reference sample memory, the reference blockmay be padded using a reference sample line in the left CTU and/or a topCTU. Therefore, the block vector can be valid even when the block vectorpoints to an unavailable reference block.

At (S1530), at least a sample of the current block is reconstructedbased on padded values of the reference block. When reference samples ofthe reference block are not stored in the reference sample memory, thereference block may be padded using a reference sample line in the leftCTU or a top CTU. The padded values may be stored in a memory that isdifferent from the reference sample memory. Therefore, at least a sampleof the current block may be reconstructed based on padded values of thereference block. After (S1530), the process proceeds to (S1599) andterminates.

V. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 16 shows a computersystem (1600) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 16 for computer system (1600) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1600).

Computer system (1600) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1601), mouse (1602), trackpad (1603), touchscreen (1610), data-glove (not shown), joystick (1605), microphone(1606), scanner (1607), camera (1608).

Computer system (1600) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1610), data-glove (not shown), or joystick (1605), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1609), headphones(not depicted)), visual output devices (such as screens (1610) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability-some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1600) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1620) with CD/DVD or the like media (1621), thumb-drive (1622),removable hard drive or solid state drive (1623), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1600) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1649) (such as, for example USB ports of thecomputer system (1600)); others are commonly integrated into the core ofthe computer system (1600) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1600) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1640) of thecomputer system (1600).

The core (1640) can include one or more Central Processing Units (CPU)(1641), Graphics Processing Units (GPU) (1642), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1643), hardware accelerators for certain tasks (1644), and so forth.These devices, along with Read-only memory (ROM) (1645), Random-accessmemory (1646), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1647), may be connectedthrough a system bus (1648). In some computer systems, the system bus(1648) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1648),or through a peripheral bus (1649). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1641), GPUs (1642), FPGAs (1643), and accelerators (1644) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1645) or RAM (1646). Transitional data can be also be stored in RAM(1646), whereas permanent data can be stored for example, in theinternal mass storage (1647). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1641), GPU (1642), massstorage (1647), ROM (1645), RAM (1646), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1600), and specifically the core (1640) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1640) that are of non-transitorynature, such as core-internal mass storage (1647) or ROM (1645). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1640). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1640) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1646) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1644)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

Appendix A: Acronyms

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit-   IBC: Intra Block Copy-   CPR: Current Picture Referencing-   BV: Block Vector-   AMVP: Advanced Motion Vector Prediction-   HEVC SCC: HEVC Screen Content Coding-   DPB: Decoded Picture Buffer-   QT: Quaternary-Tree-   BT: Binary-Tree-   TT: Ternary-Tree-   TL: top-left-   TR: top-right-   BL: bottom-left-   BR: bottom-right

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information of a current block in acurrent coding tree unit (CTU) from a coded video bitstream, theprediction information indicating an intra block copy (IBC) mode;determining which of a combination of vertical padding and horizontalpadding is performed to determine padded values of a reference block ina neighboring left CTU included in a fixed search range of blocks in thecurrent CTU; determining the padded values based on a block vector thatpoints to the reference block and a position of the current block in theCTU, the padded values of the reference block being copied from at leastone reference sample line according to the determination of which of thevertical padding and the horizontal padding is performed, availabilityof reference blocks in the fixed search range varying for each of theblocks in the current CTU; and reconstructing at least a sample of thecurrent block based on one of (i) the padded values of the referenceblock and (ii) reconstructed samples of the reference block based on theavailability of the reference block in the fixed search range, whereinthe left CTU is padded using a combination of the vertical and thehorizontal padding.
 2. The method of claim 1, wherein the reconstructedsamples of the reference block are not stored in a reference samplememory, and the padded values of the reference block are stored in amemory that is different from the reference sample memory.
 3. The methodof claim 1, wherein the current CTU is partitioned into a top-leftcoding region, a top-right coding region, a bottom-left coding region,and a bottom-right coding region, and the current block is in any one ofthe top-left coding region, the top-right coding region, the bottom-leftcoding region, and the bottom-right coding region of the current CTU. 4.The method of claim 1, wherein the reference block is padded verticallyby the reference sample line above the current CTU or horizontally bythe reference sample line to the left of the current CTU.
 5. The methodof claim 2, wherein when a maximum size of the reference sample memoryis limited to four sets of 64×64 luma samples and corresponding chromasamples, the reference sample memory stores reconstructed samples of acurrent 64×64 coding region and reconstructed samples of three 64×64reference coding regions, each of the three 64×64 reference codingregions being either in one of the current CTU and the left CTU, and thethree 64×64 reference coding regions do not include all thereconstructed samples of the reference block.
 6. The method of claim 2,wherein the left CTU is partitioned into a top-left reference codingregion, a top-right reference coding region, a bottom-left referencecoding region, and a bottom-right reference coding region, and each ofthe reference coding regions in the left CTU including reconstructedsamples that are not stored in the reference sample memory is padded bythe reference sample line above the current CTU or to the left of thecurrent CTU.
 7. The method of claim 2, wherein the left CTU ispartitioned into a top-left reference coding region, a top-rightreference coding region, a bottom-left reference coding region, and abottom-right reference coding region, and the reference block isincluded in the top-right reference coding region or the bottom-rightreference coding region of the left CTU, or in the current CTU.
 8. Themethod of claim 7, wherein when a maximum size of the reference samplememory is limited to three sets of 64×64 luma samples and correspondingchroma samples, the reference sample memory stores reconstructed samplesof a current 64×64 coding region and reconstructed samples of two 64×64reference coding regions, each of the two 64×64 reference coding regionsbeing either in one of the current CTU and the left CTU, and the two64×64 reference coding regions do not include all the reconstructedsamples of the reference block.
 9. The method of claim 7, wherein eachof the top-right reference coding region of the left CTU, thebottom-right reference coding region of the left CTU, and referencecoding regions in the current CTU including reconstructed samples thatare not stored in the reference sample memory is padded by the referencesample line above the current CTU or to the left of the current CTU. 10.The method of claim 7, wherein when a maximum size of the referencesample memory is limited to two sets of 64×64 luma samples andcorresponding chroma samples, the reference sample memory storesreconstructed samples of a current 64×64 coding region and reconstructedsamples of one 64×64 reference coding region in one of the current CTUor the left CTU, and the 64×64 reference coding region includes all thereconstructed samples of the reference block.
 11. The method of claim10, wherein each of the top-right reference coding region of the leftCTU, the bottom-right reference coding region of the left CTU, andreference coding regions in the current CTU including reconstructedsamples that are not stored in the reference sample memory is padded bythe reference sample line above the current CTU or to the left of thecurrent CTU.
 12. The method of claim 1, wherein each of a plurality ofreference coding regions of the current CTU and the left CTU are paddedhorizontally by a first reference sample line above the current CTU orvertically by a second reference sample line to the left of the currentCTU based on (i) a first distance between each of the plurality of thereference coding regions and the first reference sample line above thecurrent CTU and (ii) a second distance between each of the plurality ofthe reference coding regions and the second reference sample line to theleft of the current CTU.
 13. The method of claim 2, wherein thereference block is padded by boundary pixels of a reconstructedreference block in one of the current CTU and the left CTU, andreconstructed samples of the reconstructed reference block are stored inthe reference sample memory.
 14. An apparatus, comprising: processingcircuitry configured to decode prediction information of a current blockin a current coding tree unit (CTU) from a coded video bitstream, theprediction information indicating an intra block copy (IBC) mode;determine which of a combination of vertical padding and horizontalpadding is performed to determine padded values of a reference block ina neighboring left CTU included in a fixed search range of blocks in thecurrent CTU; determine the padded values based on a block vector thatpoints to the reference block and a position of the current block in theCTU, the padded values of the reference block being copied from at leastone reference sample line according to the determination of which of thevertical padding and the horizontal padding is performed, availabilityof reference blocks in the fixed search range varying for each of theblocks in the current CTU; and reconstruct at least a sample of thecurrent block based on one of (i) the padded values of the referenceblock and (ii) reconstructed samples of the reference block based on theavailability of the reference block in the fixed search range, whereinthe left CTU is padded using a combination of the vertical and thehorizontal padding.
 15. The apparatus according to claim 14, wherein thereconstructed samples of the reference block are not stored in areference sample memory, and the padded values of the reference blockare stored in a memory that is different from the reference samplememory.
 16. The apparatus according to claim 14, wherein the current CTUis partitioned into a top-left coding region, a top-right coding region,a bottom-left coding region, and a bottom-right coding region, and thecurrent block is in any one of the top-left coding region, the top-rightcoding region, the bottom-left coding region, and the bottom-rightcoding region of the current CTU.
 17. The apparatus according to claim14, wherein the reference block is padded vertically by the referencesample line above the current CTU or horizontally by the referencesample line to the left of the current CTU.
 18. The apparatus accordingto claim 15, wherein when a maximum size of the reference sample memoryis limited to four sets of 64×64 luma samples and corresponding chromasamples, the reference sample memory stores reconstructed samples of acurrent 64×64 coding region and reconstructed samples of three 64×64reference coding regions, each of the three 64×64 reference codingregions being either in one of the current CTU and the left CTU, and thethree 64×64 reference coding regions do not include all thereconstructed samples of the reference block.
 19. The apparatusaccording to claim 15, wherein the left CTU is partitioned into atop-left reference coding region, a top-right reference coding region, abottom-left reference coding region, and a bottom-right reference codingregion, and each of the reference coding regions in the left CTUincluding reconstructed samples that are not stored in the referencesample memory is padded by the reference sample line above the currentCTU or to the left of the current CTU.
 20. A non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform: decodingprediction information of a current block in a current coding tree unit(CTU) from a coded video bitstream, the prediction informationindicating an intra block copy (IBC) mode; determining which of acombination of vertical padding and horizontal padding is performed todetermine padded values of a reference block in a neighboring left CTUincluded in a fixed search range of blocks in the current CTU;determining the padded values based on a block vector that points to thereference block and a position of the current block in the CTU, thepadded values of the reference block being copied from at least onereference sample line according to the determination of which of thevertical padding and the horizontal padding is performed, availabilityof reference blocks in the fixed search range varying for each of theblocks in the current CTU; and reconstructing at least a sample of thecurrent block based on one of (i) the padded values of the referenceblock and (ii) reconstructed samples of the reference block based on theavailability of the reference block in the fixed search range, whereinthe left CTU is padded using a combination of the vertical and thehorizontal padding.